Liquid crystal display device with an organic insulating layer having a uniform undamaged surface

ABSTRACT

A method for manufacturing a liquid crystal display having a TFT functioning as a switching element and a passivation layer covering the TFTs and a pixel electrode connected to an output electrode of the TFT on the passivation layer, the method including the steps of coating a photo resist on the passivation layer so that the photo resist has a thickness of more than about 1.2 times of the passivation layer, patterning the photo resist to have a predetermined shape, etching the passivation layer according to the patterned photo resist, removing the remaining photo resist and treating the surface of the passivation layer to be a SiO 2  thin layer on the passivation layer using O 2  gas, forming a pixel electrode on the passivation layer by depositing and patterning an ITO layer.

This is a division of U.S. application Ser. No. 09/213,705 filed Dec. 17, 1998 now U.S. Pat. No. 6,335,781.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of patterning a pixel electrode of a liquid crystal display (LCD) device including a switching element for driving and controlling a liquid crystal. More specifically, the present invention relates to a patterning method for manufacturing a liquid crystal display having a TFT (thin film transistors) functioning as a switching element in which a passivation layer covers the TFT and a pixel electrode is connected to an output electrode of the TFT on the passivation layer, and also relates to a structure of a liquid crystal display device manufactured by this method.

2. Description of the Background Art

Conventionally, an LCD has a structure as shown in FIG. 1 which illustrates a plane view of an enlarged LCD panel. A gate line 17 is arranged to extend in a horizontal direction and a data line 15 is arranged to extend in a vertical direction which crosses the gate line 17 perpendicularly. At the intersection portion of the gate line 17 and the data line 15, a TFT including a gate electrode 17 a, a source electrode 15 a, a drain electrode 15 b and a semiconductor layer 22 is formed. A passivation layer (not shown) is formed thereon. A pixel electrode 4 connected to the drain electrode 15b is formed on the passivation layer.

When patterning the pixel electrode 4 according to the conventional method, the actual patterned shape is often different from the originally designed shape or desired shape. FIG. 2 shows the typically distorted shape of the pixel electrode 4 after being patterned by the conventional method.

The dotted line 55 in FIG. 2 is the boundary of the originally designed shape of the pixel electrode 4. As seen in FIG. 2, the pixel electrode 4 has a distorted boundary portion having a width W2 and tearing-off portions 20 in the pixel electrode. Here, W₁ is a width of the data line 15.

Referring to FIGS. 3a-3 j which are cross-sectional views cut along the a—a line of the FIG. 1, a conventional method for manufacturing the LCD will be explained in order to illustrate the reason for the pixel electrode having an undesired pattern shown in FIG. 2.

On a transparent substrate 11, a metal selected from the group of aluminum (Al), aluminum alloy, chromium (Cr) or molybdenum (Mo) is deposited to form a first metal layer 50. A photo resist 51 is coated on the first metal layer 50 as shown in FIG. 3a.

The photo resist 51 is patterned to have a predetermined shape. Using a wet etching method, the first metal layer 50 is patterned according to the shape of the photo resist 51 to form a gate line (not shown) and to form a gate electrode 17 a which is derived from the gate line. Then the remaining photo resist on the gate line and the gate electrode 17 a is removed as shown in FIG. 3b. The gate electrode 17 a can be anodized to eliminate hillocks thereon. In addition, the cross-sectional shape of the gate electrode 17 a preferably has a tapered shape.

On the substrate having the gate electrode 17 a, a gate insulating layer 23 including an inorganic insulating material such as SiN_(x) or SiO_(x), an amorphous silicon (or a-Si) 52 and an n⁺ type impurity doped a-Si (or N⁺ type a-Si) 53 are sequentially deposited. A photo second resist 61 is coated thereon as shown in FIG. 3c.

The second photo resist 61 is patterned to have a predetermined shape. According to the patterned second photo resist 61, the a-Si material 52 and the n⁺ type a-Si material 53 are simultaneously etched to form a semiconductor layer 22 and an ohmic contact layer 25. The remaining second photo resist 61 on the ohmic contact layer 25 is removed as shown in FIG. 3d.

A second metal layer 54 including chromium or aluminum is deposited and a third photo resist 63 is coated on the second metal layer 54 as shown in FIG. 3e.

The third photo resist 63 is patterned to have a predetermined shape. According to the patterned third photo resist 63, the second metal layer 54 is patterned via a wet etching method to form a data line 15. At the same time, a source electrode 15 a derived from the data line 15 and a drain electrode 15 b which faces the source electrode 15 a are formed on the ohmic contact layer 25 whereas the source electrode 15 a and the drain electrode 15 b are separated via a distance. The n⁺ type a-Si material 53 between the source electrode 15 a and the drain electrode 15 b is removed via a dry etching method using the source electrode 15 a and the drain electrode 15 b as a mask. The remaining photo resist on the source electrode 15 a and the drain electrode 15 b is removed as shown in FIG. 3f.

A passivation layer 26 including an organic material such as BCB (or benzocyclobutene) is coated thereon via a spin coating method. A fourth photo resist 65 is coated so as to have a thickness that is less than a thickness of the passivation layer 26 as shown in FIG. 3g.

The fourth photo resist 65 is patterned to have a predetermined shape. According to the patterned fourth photo resist 65, the passivation layer 26 is patterned via a dry etching method to form a contact hole 30 which exposes a portion of the drain electrode 15 b. The remaining fourth photo resist 65 on the passivation layer 26 is removed as shown in FIG. 3h.

On the passivation layer 26, an ITO(or Indium Tin Oxide) 55 is deposited so as to have a thickness of about 500 Å. On the ITO layer 55, a fifth photo resist 67 is coated as shown in FIG. 3i.

The fifth photo resist 67 is patterned to have a predetermined shape. According to the patterned fifth photo resist 67, the ITO layer 55 is patterned via a wet etching method to form a pixel electrode 4 as shown in FIG. 3j.

In the above mentioned conventional method, because the passivation layer 26 has a lower dielectric constant (lower than 3.0) than the inorganic material and forms an organic insulating layer(BCB) which can even a surface property thereof, the pixel electrode 4 disposed on the passivation layer can be overlapped with the data line 15 so that the aperture ratio can be maximized.

However, after the passivation layer 26 including an organic material such as BCB is patterned by using the fourth photo resist 65 as shown in FIGS. 3g and 3 h, the surface of the patterned passivation layer 26 can be rough and uneven.

If the pixel electrode 4 is formed on the uneven surface of the passivation layer 26, the patterned pixel electrode 4 has distorted edge portions and tearing-off portions as shown in FIG. 2.

The cause of the formation of the distorted pattern is explained hereafter in detail.

When the passivation layer having an Si bond structure such as BCB is patterned, the substrate which has the passivation layer and patterned photo resist is inserted into an etching chamber filled with an etching gas such as O₂/SF₆ or O₂/CF₄. The portions of the passivation layer exposed through the patterned photo resist are removed by changing a volatile material SiF4 according to the chemical reaction of the Si functional group of the passivation layer and the F radical of the SF₆ or CF₄. At the same time, the photo resist is removed by etching with O₂ gas.

As the etching speed of the passivation layer and the etching speed of the photo resist is similar, the thickness of the photo resist is the same as that of the passivation layer. So, when the patterning of the passivation layer is finished, the photo resist is almost completely removed.

However, it is very difficult to coat the photo resist to have a uniform thickness. Therefore, after the patterning of the passivation layer is finished, the portions where the photo resist is thicker have some remaining photo resist. Otherwise, at the portion where the photo resist is thinner, some surfaces of the passivation layer are over-etched by the etching gas as shown in FIG. 4.

For example, when O₂/CF₄ is used as the etching gas, the ratio of the composed atoms at the surface of the over etched passivation layer is determined to be Si:C:O:F=2-3:58:24:10. Even if the surface is treated with O₂ gas, the surface of the passivation layer is still uneven because of the F radical.

If the ITO layer is deposited on the uneven passivation layer, the ITO is not deposited at the convex portions 20 which have the extruded passivation layer as shown in FIG. 5. A photo resist is then deposited and patterned on the ITO layer 60 which is not uniformly deposited. When the ITO layer 60 is patterned according to the patterned photo resist, the pixel electrode does not have the originally designed shape. For example, the edges of the pixel electrode 4 do not reach the portion A and therefore, the edge of the pixel electrode has a reduced width W.

Therefore, the aperture ratio of the pixel electrode cannot be maximized. Furthermore, since the tearing-off portion of the pixel electrode does not generate an electrical field for driving the liquid crystal, the picture quality is inferior.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of the present invention provide a method for patterning a thin layer to have an originally designed shape. Preferred embodiments of the present invention also provide a method for patterning a pixel electrode to have an originally designed shape. Another preferred embodiment of the present invention provides a method for manufacturing an LCD having a pixel electrode of which an aperture ratio is maximized. In addition, another preferred embodiment of the present invention provides a method for manufacturing the LCD which has a high picture quality resulting from a desired patterning of the pixel electrode.

In order to overcome problems with the conventional method and to achieve the advantages described in the preceding paragraph, preferred embodiments of the present invention provide a method of patterning the passivation layer which includes the steps of coating a photo resist to have a thickness of more than about 1.2 times of a thickness of the passivation layer, patterning the photo resist to have a predetermined shape, etching the passivation layer according to the patterned photo resist, removing the remaining photo resist and treating the surface of the passivation layer so as to form an SiO₂ thin layer on the passivation layer using O₂ gas and forming a pixel electrode on the passivation layer by depositing and patterning an ITO layer.

According to preferred embodiments of the present invention, even after the patterning of the passivation layer is finished, a thin photo resist layer still covers the passivation layer. Because the photo resist is about 1.2 times thicker than the passivation layer when patterning starts, all surfaces of the patterned passivation layer can be covered by the photo resist, after patterning ends even if the thickness of the photo resist is not uniform. Therefore, the passivation layer does not contact the etching gas so that the passivation layer is not over-etched by the etching gas.

After that, the remaining photo resist is removed via ashing with O₂. Then preferably, the ashing process continuously treats some surfaces of the passivation layer so that a thin SiO₂ layer is formed on the passivation layer.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

The present invention will be more fully understood from the detailed description given hereafter and the accompanying drawings which are provided as a way of illustration only and therefor not limited to the present invention and wherein:

FIG. 1 is a plane view of the conventional liquid crystal display device;

FIG. 2 is a plane view illustrating the pixel electrode having a distorted edge portion and tearing-off portions therein according to the conventional method;

FIGS. 3a-3 j show cross-sectional views for explaining a conventional method of manufacturing the liquid crystal display;

FIG. 4 is a cross-sectional view illustrating the uneven surface of the passivation layer after patterning according to the conventional method;

FIG. 5 is a cross-sectional view illustrating the patterned pixel electrode having an undesired patterning result according to the conventional method;

FIG. 6 is a plane view of a liquid crystal display according to a preferred embodiment of the present invention; and

FIGS. 7a-7 e show cross-sectional views for explaining a method for manufacturing a liquid crystal display according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to the figures, preferred embodiments of the present invention will be explained in detail. FIG. 6 is a plane view of a liquid crystal display having a pixel electrode patterned according to an original design of a preferred embodiment of the present invention. FIGS. 7a-7 e are cross-sectional views showing a method for manufacturing a liquid crystal display which is cut along the VIIa-VIIe line of the FIG. 6.

On a transparent substrate 111, a gate electrode 117 a derived from a gate line 117, a gate insulating layer 123, a semiconductor layer 122 and an ohmic contact layer 125, a source electrode 115 a derived from a data line 115, and a drain electrode 115 b are formed by the same conventional method as described above.

A passivation layer 126 including an organic material such as BCB is coated on the entire surface of the substrate 111 having the source 115 a and the drain electrode 115 b. A photo resist 151 is coated on the passivation layer 126 which is about 1.2 times thicker than the passivation layer 126. The photo resist 151 is patterned so as to have a predetermined shape wherein a contact hole for exposing the drain electrode 115 b is formed as shown in FIG. 7a.

The substrate 111 having the patterned photo resist 151 is inserted into an etching chamber which is filled with O₂/SF₆ gas or O₂/CF₄ gas. Then, the exposed portions of the passivation layer start to be removed by changing into a volatile material SiF₄ which is generated by the chemical reaction of the Si functional group of the passivation layer and F radical of the SF₆ or CF₄ gas. As a result, a contact hole 130 exposing some portions of the drain electrode 115 b is formed.

At the same time, the photo resist 151 starts to be ashed by the O₂ gas. Since the etching speed of the passivation layer 126 and the ashing speed of the photo resist are similar to each other, when the contact hole is formed, the photo resist having a thickness which is about 0.2 times that of the passivation layer remains as shown in FIG. 7b.

After removing the SF₆ or CF₄ gas from the etching chamber, the remaining photo resist is removed by ashing with only O₂ gas. After all of the photo resist material is removed, the ashing step is performed continuously in order to form a thin SiO₂ layer 170 on the passivation layer by ashing with the O₂ gas as shown in FIG. 7c.

In another method, the remaining photo resist is removed by using an organic mixture solution including NMP (or N-Methyl-Pyrrolidone), alcohol and amine, then a SiO₂ thin layer 170 is formed by treating the surface of the passivation layer with O₂ gas.

As a result of preferred embodiments of the present invention, the passivation layer is not exposed to the SF₆ or CF₄, so the passivation layer is not over-etched by these gases and as a result, the passivation layer has a uniform surface. For example, when O₂/CF₄ gas is used for an etching gas, the ratio of the composed atoms at the surface of the over-etched passivation layer is determined to be Si:C:O:F=24.3:21.6:52.3:0. According to the atom ratio, the surface of the passivation layer does not react with the F radical of the CF₄.

In this preferred embodiment, even though the etching gas is either SF₆ gas and CF₄ gas, the etching gas can be changed according to the material of the passivation layer.

On the entire surface of the substrate 111 having the contact hole 130, an ITO (Indium Tin Oxide) 156 is deposited so as to have a thickness of about 500 Å. Another photo resist 161 is coated on the ITO layer 156 and patterned to have a predetermined shape as shown in FIG. 7d.

According to the patterned photo resist 161, the ITO layer 156 is patterned via wet etching method to form a pixel electrode 104. Because the passivation layer has a low dielectric constant (lower than 3.0) and an even surface, the pixel electrode 104 can be overlapped with some portions of the data line and gate line.

As described above, according to preferred embodiments of the present invention, because the photo resist for patterning the passivation layer is thicker than that of the passivation layer, even though the patterning of the passivation layer is finished, the photo resist still prevents the passivation layer from reacting with the etching gas. Therefore, the passivation layer has a uniform surface after the patterning.

So, the pixel electrode formed on the passivation layer can be patterned to have an originally designed shape. Therefore, the LCD includes a pixel electrode having a maximum aperture ratio and an excellent quality of the picture.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the forgoing and other changes in form and details may be made therein without departing from the spirit of the invention. 

What is claimed is:
 1. A liquid crystal display device comprising: a substrate having a gate line, a data line and a switching element; an organic insulating layer covering the substrate and having a uniform undamaged surface which is unaffected by an etchant, the organic insulting layer being patterned with a photoresist having a thickness of more than 1.2 times of a thickness of the organic insulating layer; and a pixel electrode on the organic insulating layer.
 2. The liquid crystal display of claim 1, wherein the organic insulating layer has an Si bond structure.
 3. The liquid crystal display of claim 1, wherein the organic insulating layer comprises benzocyclobutene.
 4. The liquid crystal display of claim 1, wherein the etchant comprises at least one of CF₄ gas and SF₆ gas.
 5. The liquid crystal of claim 1, further comprising a thin SiO₂ layer between the organic insulating layer and the pixel electrode.
 6. The liquid crystal display of claim 1, wherein the pixel electrode overlaps at least one of the data line and the gate line.
 7. The liquid crystal display of claim 1, wherein the organic insulating layer is not exposed to SF₆ or CF₄.
 8. The liquid crystal display of claim 1, wherein the organic insulating layer does not react with an F radical.
 9. The liquid crystal display of claim 1, wherein the organic insulating layer has atoms at a surface thereof having a ratio Si:C:F=24.3:21.6:52.3:0.
 10. The liquid crystal display of claim 1, wherein the organic insulating layer has a dielectric constant lower than 3.0. 